1. Field of the Invention
This invention relates to dental retainers or appliances for straightening and retaining teeth and more particularly, to a thermoformed plastic dental retainer and method of construction including rapid, typically refrigerant-induced cooling of the retainer as the retainer sets on a dental impression cast which is constructed from an impression of a patient""s upper or lower dentition. Using a sheet, plate or disc of thermoformable plastic and a vacuum or pressure thermoforning machine, the retainer is initially vacuum-thermoformed over the dental impression cast. As the thermoformed plastic retainer sets on the cast, a refrigerant coolant, particularly 1,1,1,2-tetrafluoroethane, is typically sprayed on the retainer. The rapid cooling of retainer on the cast, induced by the coolant, causes the retainer to thermally contract against the cast and precisely conform to the configuration and texture of the cast, and thus fit more accurately and tightly on the patient""s dentition during treatment. Protrusions or divots may be formed in the retainer and gaps, openings or windows formed in the retainer on the opposite sides of the respective divots to accommodate unhindered tooth repositioning movement as the divots apply repositioning pressure to maloccluded or crooked teeth while the retainer is worn on the patient""s dentition over a period of days or weeks.
2. Description of the Prior Art
A xe2x80x9cThermoformed Plastic Dental Retainer and Method of Constructionxe2x80x9d is described in my U.S. Pat. No. 5,692,894, dated Dec. 2, 1997. The dental retainer is constructed by first forming an impression of a patient""s upper or lower dentition and constructing a cast from the impression The retainer is vacuum thermoformed over the cast using a sheet, plate or disc of thermoformable plastic and a vacuum or pressure thermoforming machine. A protrusion or divot is formed in the retainer on the labial or lingual side of each tooth which is to be repositioned lingually or labially, respectively, and a gap, opening or window is formed in the retainer on the opposite side of the divot to accommodate unhindered tooth repositioning movement. As the retainer is worn on the patient""s dentition over a period of days or weeks, the projecting divots apply pressure to the respective teeth and push the teeth into the gap or window of the retainer to a straightened position. By appropriately positioning the divots in the retainer with respect to the patient""s malpositioned teeth, the teeth can be moved labially, lingually or rotated, as needed, for straightening.
The thermoformable plastic dental retainer described in my U.S. Pat. No. 5,692,894 represents a considerable improvement over conventional teeth straightening and retaining devices, in several respects. The retainer can be used to retain the dentition of finished orthodontic cases at a fraction of the cost and with fewer problems than conventional devices. Unlike conventional wire braces, the clear retainer is aesthetically-pleasing to the patient and usually requires no periodic adjustment, thus affording the clinician significant relief in chair time and administrative detail It has surprisingly been found that rapidly cooling the thermoformed retainer as the retainer sets on the cast, such as by spraying a refrigerant coolant on the retainer, causes thermal contraction of the retainer against the cast and the retainer to more precisely conform to the configuration and texture of the cast and thus, the patient""s mouth than is the case when the cooling step is omitted. The retainer thus more accurately fits in the patient""s mouth throughout extended wearing of the retainer during treatment.
It is therefore an object of this invention to provide a new and improved thermoformed plastic dental retainer and method of construction of the retainer.
Another object of this invention is to provide a new and improved thermoformed plastic dental retainer which more precisely conforms to the configuration and texture of a patient""s dentition.
Still another object of this invention is to provide a thermoformed plastic dental retainer and method of construction the retainer including rapidly cooling the thermoformed retainer as the retainer sets on a dental impression cast constructed from an impression of a patient""s upper or lower dentition.
Yet another object of this invention is to provide a thermoformed plastic dental retainer and method of construction of the dental retainer, including forming an impression of a patient""s upper or lower dentition and constructing a cast from the impression; vacuum-thermoforming the retainer over the cast using a sheet, plate or disc of thermoformable plastic and a vacuum or pressure thermoforming machine; and rapidly cooling the retainer typically by applying a refrigerant coolant to the retainer as the retainer sets on the cast, whereby the rapidly-cooling retainer thermally contracts against the dental impression cast and precisely conforms to the configuration and texture of the cast, to accurately and snugly fit on the patient""s dentition during treatment.
These and other objects of the invention are provided in a thermoformed plastic dental retainer and method of construction including rapid cooling of the retainer, typically using a refrigerant coolant, as the retainer sets on a dental impression cast. The dental retainer is constructed by first forming an impression of a patient""s upper or lower dentition and constructing a cast from the impression. The retainer is vacuum-thermoformed over the cast using a sheet, plate or disc of thermoformable plastic and a vacuum or pressure thermoforming machine. As the thermoformed plastic retainer sets on the cast, the retainer is rapidly cooled typically by spraying a refrigerant coolant, such as 1,1,1,2-tetrafluoroethane, on the retainer. This step causes thermal contraction of the rapidly-cooling retainer against the cast, and the retainer precisely conforms to the configuration and texture of the cast and thus, achieves a more accurate and tighter fit on the patient""s dentition during treatment. Protrusions or divots may be formed in the retainer and gaps, openings or windows formed in the retainer on the opposite sides of the respective divots to accommodate unhindered tooth repositioning movement as the divots apply corrective pressure to maloccluded teeth while the retainer is worn on the patient""s dentition over a period of days or weeks.